With focusing devices, which include binoculars, monoculars, field glasses, and telescopes, there are different distances between the eyepiece lenses and eyeballs that are comfortable to the users due to the differences in their vision. Therefore, the eyepieces (the part that is in contact with eyes) of binoculars are often equipped with variable focusing devices (e.g., twist-up devices), that can adjust the distance between the eyepiece lenses and eyeballs.
A commonly used twist-up device is basically composed of a twist-up ring and a support ring that is often called a split-image suppressor ring. The twist-up ring has a longer twist-up adjustment groove, and the support ring is contained inside the twist-up ring, and it is equipped with the twist-up adjustment pins that are inserted into the above twist-up adjustment groove. The twist-up device moves the twist-up adjustment pins inside the twist-up adjustment groove along its circumference, and it twists up by moving the twist-up ring against the support ring in the adjustment groove. In so doing, the distance between the eyepiece lenses and eyeballs is made larger or smaller by the distance that the twist-up ring has moved.
The twist-up adjustment groove in the conventional twist-up ring is set in a straight line, diagonally from the opening at one end to the opening at the other end of the twist-up ring. For this reason, when the conventional twist-up device was operated by moving the twist-up ring against the support ring so that the pin slides along the groove to a desired position. However, there is no means known in the art to fix the twist-up ring at a fixed position. Consequently, when the twist-up ring is pressed against the eyeballs to look at something, the pin tends to slide in the groove and the twist-up ring consequently rotates, and it was not possible to maintain the desired position originally obtained by manipulating the twist-up device. As a result, a focusing device with the conventional twist-up devices known in the art fail to secure a proper distance between the eyepiece lenses and eyeballs which causes images to lose focus, difficulty in seeing desired objects and other inconveniences to the user.
In an attempt to resolve this limitation in the art, a twist-up device has been developed with a retaining section using a spring-operated retaining ball in the support ring, which can be pushed against the twist-up ring and held steady in the twist-up adjustment groove of the twist-up ring. With this twist-up device, when the twist-up ring is moved along the support ring in a set groove and the retaining ball comes to the set position in the retaining section and remains in the retaining section by the spring action. As a result, the retaining ball restricts the twist-up ring from moving to the direction of the groove. Thus, this twist-up device is able to prevent the movement of the twist-up ring when the user was looking at something through the focusing device, such as a binocular or other device as mentioned above.
However, there are limitations to the art of twist-up devices having a restraining ball and spring. The above retaining ball is held in place only the spring force. So, when a force applied to the focusing device is stronger than the spring force applied to the twist-up device, the retaining ball comes off of the retaining section, and the twist-up ring moves thereby failing to maintain the desired position obtained by manipulating the twist-up device, which is a significant shortcoming.
Another limitation to twist-up devices having a retaining ball and spring is the increased number of parts required for manufacturing the devices in addition to using the device. Additionally, a special manufacturing process is necessary to secure the above-mentioned retaining function. The increased number of parts complicates the manufacturing process, increases the manufacturing costs, and increase the number of components which may potentially fail. These are further shortcomings in the art.
The objectives of the present invention are to solve or avoid the above shortcomings held by the conventional twist-up devices. In other words, the objectives of the present invention are to make it possible to securely maintain the adjustment position obtained by manipulating the twist-up device even when a force is applied while focusing device is in use, to limit the number of parts to as few as possible, to enhance the ability of the focus device to remain in focus with increased force applied to the focusing device, and to provide a twist-up device with its manufacturing cost kept low.